A recent concern in mental health delivery has been what has been termed the "criminalization of the mentally-ill"; it is speculated that a number of persons who had heretofore been treated within the mental health system have, as a result of changes in legal and social policy, come under the purview of the criminal justice system. Although there have been several studies showing an increase in the numbers of mentally disordered persons in jails, previous research in this area has been inadequate to establish conclusively the extent of this problem. Specifically, the research literature has suffered from imprecise measurement as well as insufficient sample size. The proposed research will move beyond the previous research in two ways: first, the extent of mental illness among one urban jail (Cook County Jail in this case) will be assessed using the NIMH-DIS instrument; N = 700. Second, the research will explore the extent to which persons exhibiting signs of mental disorder are detected and given psychiatric treatment. The results of this research are expected to add important knowledge relative to the extent of the alleged "criminalization of the mentally ill". In so doing, the findings will aid in planning needed changes in mental health delivery for jail populations, as well as suggest viable alternatives to incarceration for mentally-disordered offenders.